In many applications, it can be difficult to directly connect a die to another circuit or substrate, such as a printed circuit board (PCB). For example, if an integrated circuit is to be mounted on a PCB, wiring of the PCB may be too coarse to connect to the fine contacts of the integrated circuit. In such applications, the die and PCB may be interconnected through an interposer. An interposer is a silicon body having a first set of fine contacts (e.g., micro-bumps) on one side, to which a die may be bonded, and a second set of coarse contacts (e.g., C4 solder-bumps) on the other side for bonding to another chip, substrate, PCB, etc. Wiring and vias of the interposer may connect fine-pitched die contacts located on one side of the interposer to a coarser contact array on the opposite side of the interposer. An interposer may also provide interconnections between dice that are mounted on the same side of the interposer.
For clarity and ease of reference, a top surface of an interposer, semiconductor die, substrate, or any layer thereof may be referred to as a front-side and such terms are used interchangeably herein. Similarly, a bottom surface of an interposer, semiconductor die, substrate, or any layer thereof may be referred to as a back-side, and such terms are used interchangeably herein. The front-side of the substrate is the side having the fine contacts, and the back-side of the substrate is the side having the coarse contacts.
Through-silicon vias (TSVs) are used to connect the contacts on the front-side of the interposer to contacts on the back-side of the interposer. Metallized wiring layers may also be added to connect the TSVs to the contacts on the front-side of the interposer. However, in forming TSVs in a silicon body of an interposer, the silicon body is often thinned to less than 100 μm, which may present challenges for testing the interposer.
A frequent defect encountered in the manufacture of interposers is electrically open signal paths resulting from voids in TSVs or poor connection between the TSV and adjacent contacts (e.g., connection between solder-bump and TSV). The spacing between TSV is generally large enough that shorts between TSVs are unlikely.
One challenge in interposer manufacturing technologies is the testing of TSVs in the production environment. Previous methods for testing TSVs probe each TSV from the front-side and back-side simultaneously to check for continuity. Such methods are not practical and may result in damage for thinned interposer wafers having 25 um to 100 um thickness.